For those who have read my prior posts regarding Misfire Codes on my 96 XJS 2+2 w/4.0 L..............Here we go!!

Kept getting a misfire code, which as best I can describe occurs when the vehicle is shifting through the gears and the engine is still cold.

So I

1. Replaced plugs to original factory spec
2. Installed all new coils
3. Bought used Transmission ECM (Located in Trunk)
4. Cleaned MAF
5. Made sure all air lines are tightly secured

After all of this I still kept getting the same misfire code showing up.... w/no impact on performance of the vehicle............It Runs Great!!

It usually happens within 5 minutes of starting up the car and driving a short distance.

SO..............I tried something a little different.............

1. Let the car warm up for at least 5 or more minutes before putting in gear and taking off.........NO Engine Code Light!!!!! I did this for an entire week. w/no engine light coming on.

2. This morning I started the car up...DiD Not let it warm up..... and took off.....Sure enough the Engine Light came on.


I am guessing that this issue w/Engine Light (Misfire Code) coming on has something to do with ????? O2 sensor coming up to temperature....Slightest hesitation on the trans shifting causes the Engine Light to come....Maybe too sensitive!!!

AS I STATED THE CAR RUNS GREAT!!

Anybody out there have any ideas.

Something that sends a signal back to the computer and doesn't like to do it when it is not up to temperature shifting through the Gears!!!


Thanks

Softball60/Paul

1957 XK140 Drop Head Coupe
1996 XJS 2+2 (Current Vehicle)
1989 Mercedes 560SL
Every other British Sports car known to Mankind

 

Leads me to think that the coolant sensor may not be working properly, or your ECS is bad.

Try this.

Before you start your engine when its cold. Disconnect the CTS and jump the two contacts. This will cause your engine to think that the coolant is at operating temperature. If you can then run the car with no light, it's the sensor.

 

Make sure you jump the contacts on the sensor, (#17 on the attached photo, not #18)

 

Vee,

Thanks for the input.

Is the engine coolant sensor and the ECS one (1) in the same?

Thanks

 

I'm sorry, I meant ECU, not ECS in that previous post.

 

Vee,

The ECU unit. Is this the unit in the trunk or is it the unit..I think inside the passenger side kick panel.

I replaced the unit in the trunk so I don't think this is the issue.

Thanks

Softball60/Paul

 

ECU is in the passengers footwell.

Let's stay focused on the task at hand. Unplug the harness to the sensor and jump the two contacts on the harness when the engine is cold and start driving. Do you get any codes?

 

Vee,

I have pulled the wire off the sensor and have shorted the two (2) wires.

In the morning I will fire it up and drive with no warm up.

Will respond with thread sometime tomorrow aft.

Thanks for your input.

Softball60/Paul

 

Vee,

Drove it this morning cold start, no warmpup and..............NO Light!!

I will try it again tomorrow and Friday to see if anything happens.

Will let you know.

Thanks

Softball60/Paul

 

Someone else might chime in here, but I'm not sure this is great news.


What we've learned is that your car has a problem dealing with something when it's supposedly reading from it's preset script, instead of paying attention to what the sensors are telling it. (Open Loop)


I have a similarly strange spare ECU that doesn't like to send the O2 sensors into the negative side of zero. I went though several sets of O2 sensors before I arrived at that conclusion. I'm wondering if there's something wrong with the ECU.


I wonder if the temp sensor sends it to closed loop too early?

Do you have a tool that you can use to see when the car goes into closed loop?

 

Vee,

What kind of tool are you talking about?

Thanks

Softball60/Paul

 

One (1) thing I forgot to mention is that it felt as though the idle was affected.
Seemed to idle slightly higher and upon accelleration, decelleration it seemed to respond different.

Softball60/Paul

 

By tool, I meant some kind of diagnostic reader that can indicate whether the car is in open or closed loop. One of the programs I use (Yhasi Movi Pro for Apple Laptops, no iPhone app) tells me whether the car is open or closed.

Might be useful to know.

The strange acceleration/deceleration might have something to do with the artificial temp inputs you're giving the car.

 

I don't have any equipment or programs that will do what you are asking.

Not questioning your concern but why can I make the light from not coming on when all I do is let it warm up for 5 to 10 minutes.

Not having this tool or program can you suggest a next step?

Thanks

Softball60/Paul

 

The only thing I have is a code reader.

You know something just occurred to me. I do have a code reader and I did post sometime ago a typical read out of when the Misfire Code Engine light goes on.

One of the things it stated regarding the fuel system 1 & 2.

1 is OL
2 is CL
Does this refer to Open and Closed loop?

 

Looks like it.

 

Any Ideas??

 

Something is preventing your car from going into closed loop.


I may have mentioned this before, but I had an ECU that wouldn't go closed because it wouldn't read the oxygen sensor data as a negative value, for some reason. I happened to have a spare and it turned out ok.


It's odd that only one bank is reading open. I don't know if my reader operates that way, but I'll have to check.


Without more data, I'm thinking it's the ECU. Swapping out the sensor shouldn't cost much. It's a $20 part and minimal labor, if you wanna take that out of the mix. (I would, but I doubt it'll fix it.)

 

So far, you've managed to drive the car one time with the CTS harness shorted and you haven't gotten the light.

Continue to do this to expand the sample size. 1/1 is not a good indicator of success or failure.

Furthermore, if you can plug that reader back in to see if the OL and CL data has changed, that could be useful too. I would basically check it at startup, where you could have both banks on OL; and then eventually, once the O2 sensors get hot, both banks should go into CL. Give it 10 minutes of driving? (Should take less time, but let's be safe here)

 

Thanks

Give me some time and I will report back.

Softball60/Paul